A conventional image forming apparatus, such as an ink-jet recording apparatus, ejects ink (recording material) from a plurality of nozzles (recording elements) to form an image on a recording sheet (a recording medium).
Some of the conventional image forming apparatuses include a long line head covering the length of a recording sheet in the main scanning direction. In such an image forming apparatus, the position of the line head is fixed during recording in the main scanning direction and a recording sheet is transferred in the direction (the sub scanning direction) orthogonal to the main scanning direction to form an image at high speed.
Unfortunately, the long line heads covering the width of a recording sheet have disadvantages of high manufacturing costs, low production yields and low reliability, compared to short heads. Moreover, a long line head with some broken recording elements requires the entire replacement of the expensive line head, resulting in high repair costs.
To solve the above problems, there is known an image forming apparatus including a long head formed by disposing a plurality of short heads in a main scanning direction in a state in which recording elements have an overlap region in the adjacent ends of the short heads, each of the short heads having a plurality of recording elements disposed in the main scanning direction, for example.
This structure may cause deviation of landing point of recording material and impair the image quality in the overlap region due to the misalignment between the short heads. To solve this problem, some of the conventional image forming apparatuses gradually change the ejection rates (ejection share rates) of ejecting recording material from recording elements of the short heads in the overlap region to reduce the extent of deviation of landing point of recording material (Patent Documents 1 and 2, for example).
However, an ejection defective recording element which cannot eject recording material or causes significant curved ejection of recording material in the overlap region may impair the image quality in the area corresponding to the ejection defective recording element.
To solve this problem, some of the conventional image forming apparatuses gradually change the ejection share rates of ejecting recording material from recording elements of the short heads while avoiding ejection defective recording element (Patent Document 3, for example).